The present invention relates to a device for energizing by means of a DC/AC converter a heating element of a window pane from a direct current network of a motor vehicle.
To improve the electrical power supply of a heating element, for example the heating resistor of a windshield in a motor vehicle, different solutions are known for achieving a higher heating efficiency.
From the DE-OS 37 43 316 a power supply network for a motor vehicle is known which, among other functions, also supplies energy to a heatable window pane. For this purpose, an alternating current (a.c.) voltage of 80 V maximum and at a frequency of 50 Hz is produced by means of a converter and applied via an intermediate voltage coupling circuit to the heating element of the pane. However, this prior art network system fails to provide any measures for generating an a.c. heating voltage at a given frequency which would reliably meet anti-interference regulations.
From the DE-OS 26 42 028 known is the generation of an alternating current voltage from a direct current voltage by means of a resonant circuit, for example a parallel resonant circuit. In order to deliver an a.c. power at higher frequencies, the source of d.c. voltage is coupled to the load via the resonant circuit whereby an electronic switching element, for instance a switching semiconductor is connected between the d.c. voltage source and the resonant circuit. An inductance is connected in series with the switching semiconductor element. With such an alternating current generator, also called a resonant converter, the inductive heating of a resistor, for example, can be achieved. This known resonant converter also fails to meet the anti-interference requirements.